In large gas turbine engines, both the compressor section and a turbine section are of axial flow design, and each stage comprises a disk having a plurality of airfoils mounted on its rim. These blade and disk assemblies have been produced from separate components with the disk having the blades mechanically attached. This is advantageous since it permits blades to be readily replaced, but adds substantially to the weight of the assembly and it is difficult to achieve the high strength required for high speed modern gas turbine engines.
Integrally bladed rotors have been therefore developed where the blades are an integral part of the rotor. These blades are either formed integrally with the disk or are metallurgically bonded to the disk.
U.S. Pat. No. 4,873,751 entitled "Fabrication or Repair Technique for Integrally Bladed Rotor Assembly and issued Oct. 17, 1989 to Raymond M. Walker et al shows a method of bonding the blades. In accordance with the Walker et al teaching, the blade to be bonded has a collar near the end of the blade with a bonding surface. The blade fits entirely within a tool which swallows the blade and the collar, with the bonding force applies through the gripping tool. Several problems have been discovered with such a bonding method.
The same tool holder is to be used for all of the blades. Sightly oversized blades did not fit in the holder. Undersized blades were loose within the holder and moved out of position during the bond cycle.
The set up for the bonding operation had to be torn down between cycles to remove the tool, thus losing position.
Since the tool surrounds the blade, the rotor could not be rotated to the next blade stub location. Insufficient travel was available to completely withdraw the tool. Interference between the installed blade and the tool prevented the rotation.
Visual alignment is not possible with the airfoil clamped in the blade holder.
The airfoil temperature cannot be readily monitored with the airfoil clamped in the blade holder since there is no ready access to the airfoil surface.